1. Field of the Invention
The present invention relates to a suspension structure for a disk device.
2. Description of the Related Art
A hard disk device such as a magnetic disk device or the like is provided with a plurality of disks for storing information, and heads, such as MR heads or the like, for writing information to the disks and reading information from the disks. Each head is provided on a slider, and each slider is floatably disposed with respect to the disk by means of a suspension structure. Each suspension is coupled to an actuator.
A head is connected to a control circuit by lead wires which extend along the suspension. Recently, a circuit pattern has been formed on the suspension, instead of lead wires, and the circuit pattern is connected via a flexible print board to the print board of the control circuit. In this way, by forming the circuit pattern on the suspension, the disk device can be miniaturized and a high performance can be realized. Also, the circuit pattern has less influence on the suspension of the slider than leads, so that the floating characteristics of the slider are stabilized. Further, the circuit pattern can be easily connected to the head and the flexible print board, and enables easy automatic mounting of the miniaturized heads.
FIGS. 15 and 16 show a prior art suspension system. The suspension 1 comprises an attachment portion 2 for attachment onto an actuator and a tongue 3 for attaching the slider. A circuit pattern including read wiring 4R and 5R and write wiring 6W and 7W is formed on the suspension 1. The read wiring 4R and 5R is formed along one side of the suspension 1 so as to supply a read current R to a not shown head, and the write wiring 6W and 7W is formed along the other side of the suspension 1 so as to supply a write current W to the head. As shown in FIG. 16, the suspension body 1B of the suspension 1 is formed from stainless steel, and is covered by a polyimide (PI) protective coating 8. The read wiring 4R and 5R and the write wiring 6W and 7W of the copper circuit pattern are formed on the protective coating 8, and a PI protective coating 9 covers the read wiring 4R and 5R and the write wiring 6W and 7W.
In the suspension 1 having a laminated structure as shown in FIGS. 15 and 16, the coefficient of thermal expansion of stainless steel is 20 ppm, while the coefficient of thermal expansion of copper is 17.2 ppm, the difference in coefficient of thermal expansion between these metals being relatively small. However, if a localized thermal load is placed on the suspension body 1B when the disk device is operating, deformation occurs in the suspension 1 having the MR head. In particular, deformation occurs in the suspension 1 when the disk device is performing servo track writing. Deformation of the suspension 1 increases in the outer rigger region A on the side where the write current W runs, and the outer rigger region A of the suspension 1 largely deforms so that it expands, as indicated by the arrow B. If the suspension 1 deforms in this manner during servo track writing, the suspension 1 exhibits behavior such as an pivotal oscillating movement, so that, for example, after a first write cycle the position of the MR head may skip one track. This phenomenon decreases if, after application of the write current, there is a wait time of several seconds until the entire head (suspension and coil) becomes warm before writing begins, but this several seconds wait time is a hindrance in a disk device mass production line.